The idea that they're being held without charges is being used to in other words say "they can't even say what they're holding them for" - this is false, they have said what they're holding them for, they have said what the charges will be if/when charges go ahead, and they have said why they've been detained while the investigation is ongoing.
That it would be illegal in the UK isn't in dispute - he's not in the UK. He (by his own admission, again) chose not to live in the UK or similar specifically because he didn't want to live under UK law - he wanted to live somewhere corrupt where the authorities could be paid off. It seems he was either very wrong, or very right, but not as powerful as he thought. I have limited sympathy in both cases because, again, he specifically CHOSE to live in a country BECAUSE its not under the very laws that wouldn't allow him to be detained. The law in the UK is completely irrelevant.
Here's the judges reasoning;
"Last month a judge extended their detention until the end of February, citing “the capacity … of the defendants to exercise permanent psychological control over their victims, including by resorting to constant acts of violence”."
But you'll hear people saying" they've given no reason for holding them". They have. It's right there. What they're accused of is also clear. As is their flight risk. And again, UK law just isn't relevant.
Now... It is, apparently, in violation of international human rights law to hold someone for longer than 30 days without charges being made official in court (at which point people can be detained/denied bail until trial if they're considered a flight risk or a risk to the public). So the Romanian authorities may be in violation of Human Rights law but - again - that means relatively little unless its unusual for the Romanian authorities to be in violation of that law. Which I doubt it is. Again... There's a reason Tate chose to live there.
Imagine choosing to live in a country because of its reputation for not doing law by the book, getting arrested, and then your followers announcing a grand conspiracy because....... The country isn't doing law by the book. Come onnn. There's been talk for years of them either withdrawing from or being booted from the EU because they fail to comply with EU law. This isn't special treatment for Andrew Tate

.
Not least, and it takes a special kind of delusion to believe that Tate is being framed and is not a violent misogynist and a sex trafficker. He's been openly selling himself as that for years. Hint: he describes himself as a literal pimp, frequently. Pimping is sex trafficking!
"Can't believe I've been arrested on suspicion of robbing a bank, this is a conspiracy!" cried Billy Bankrobber into his sacks of stolen cash.
As a standalone concept, is detention for 2 months (at least) without formal charge a questionable thing? Absolutely. But that doesn't mean the charges proposed aren't valid, and it also doesn't mean that this is particularly unusual.
Hes a joint UK/US citizen so the government's of either country could make a diplomatic case for his release. I don't see that happening, do you? "Please let the pimp out of jail, those women consented to be trafficked and yeah I've seen the videos of physical abuse but Alf off TiBB says they probably enjoy being abused."